The invention relates to a process for controlling a dental firing furnace, in particular to a drying operation that takes place in a dental furnace.
For the drying of dental restoration parts it has been known for a long time to either use separate drying devices with infrared radiators or, to remove the moisture within dental furnaces themselves.
One example for a solution of this kind is evident from GB 332 194. In this solution it is checked whether moisture is still emitted after a period of 20 minutes by verifying if a cold mirror placed at an outlet opening, still gets steamed up.
Moreover, specific low-pressure humidity removal or dehumidification devices for the drying of dental restoration parts have become known that work with temperature sensors. With solutions of this kind, both low pressure and temperature can be measured and displayed, and the drying operation may be set according to the request and instruction of the manufacturer of the dental restoration part.
Moreover, it has also already been proposed to dry a dental restoration part during the closing operation of a firing furnace and in this connection to control the closing operation so that the drying time is sufficient, but not too long. In this connection, several sensors for determining the interior temperature of the dental furnace and further sensors can be employed, also.
The known solutions, however, have the disadvantage that as a precaution, a certain minimum time must always be adhered to, in order to ensure that a safe drying operation takes place. In this respect, the best solution despite of its age is still the solution according to the above-mentioned British patent document, since the humidity or moisture within the furnace interior is explicitly used here as a criterion for the existence of residual moisture.
With multi-unit bridges consisting of a ceramic with a specific porosity, residual moisture may remain which can considerably reduce the quality of the dental restoration part during the firing operation. A heating-up of a dental restoration part that is wet inside, for example to 700° C., would result in porosities and/or defects such as cracks that can even destroy the dental restoration part.
In order to safely prevent this effect, specific drying devices have become accepted that often work with infrared drying or curing lamps or that are configured as drying cabinets. In this respect, the dental restoration part is heated to an elevated temperature for a longer period of time such as for example one hour, in order to accelerate the drying process. In order to ensure the drying process also with larger dental restoration parts for example, a minimum time with a safety margin is experimentally preset. For the sake of convenience, said drying time also applies for different objects such as small objects or also for objects that have possibly already become dry due to a holding or exposure time, i.e., the time period between two processing operations.
It is to be understood that the evaporation temperature can be set to 100° C. only with pure water. Saline solutions may have an evaporation temperature of substantially more than 100° C., and solutions containing alcohol may have an evaporation temperature of for example only 80° C.